| Abstract | Two 3D monodisperse oligofluorenes with non-conjugated triphenylamine-based cores have been synthesized by Friedel–Crafts copolycondensation reaction. The oligomers, PF₃-TPA and PF₃-TPA₃, consist of three fluorene pentamer arms that are connected non-conjugately through a triphenylamine (TPA) and 1,3,5-tris(triphenylamino)benzene core (TPA₃), respectively, at the 9-position of the central fluorine of the pentafluorene arms. The coplanar structures of the cores and the linkages at the centre of the pentafluorene arms produced a 3D structure of oligomers. This specific structure efficiently retarded the crystallization tendencies of the pentafluorene arms and gave the materials completely amorphous morphological structures. Both oligomers emit deep-blue fluorescence with high efficiencies in thin films (Øpl–film = 67% for PF₃-TPA₃ and 86% for PF₃-TPA). The introduction of triphenylamine units into the core promoted the hole-injection ability while not obviously scarificing the electron- injection ability of the oligomers. The multi-layer devices ITO/PEDOT-PSS/PF₃-TPA₃ and PF₃-TPA/TPBI/LiF/Al were fabricated to investigate the electroluminescence (EL) properties of the two oligomers. Both oligomers showed a low turn-on voltage of 4 V. The luminances reached 1946 cd/m² at 7.5 V in the PF₃-TPA₃ device and 1055 cd/m² at 8 V in the PF₃-TPA device. The EL efficiencies at this luminance were 1.63 and 1.57 cd/A, respectively. |
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